a, Rectilineal forms of Cladothrix dichotoma in the act of passing to the zoöglœic state (stained first with solution of iodine, then with methyl violet or fuchsine), × 600. b, Beginning of the zoöglœic state of the Bacterium osteophilum (colouring with vesuvine, then with methyl‐violet, and lastly with solution of iodine), × 600.